(1) Field of the Invention
The present invention relates to a method of improving the quality of wheat flour and, more particularly, to a method which can provide wheat flour of improved quality in a very short processing time and which is entirely harmless from the viewpoint of food sanitation and safety.
In the present specification, the term "quality improvement of wheat flour" is used to generally mean improvements in various known properties of wheat flour such as improvement in the viscoelasticity of the wheat dough and improvement in the water holding capacity of the starch in the wheat flour, as well as improvements in the properties of the secondary products such as appearance and texture of cakes made from the wheat flour.
(2) Description of the Prior Art
Hitherto, various methods have been proposed and used for improvement of the quality of wheat flour. These methods broadly fall into several types as shown below.
(i) Early maturing process as disclosed in Japanese Patent Publication No. 15138/1978 (Japanese Patent No. 936,704)
This method essentially consists in preserving the wheat flour for 2 to 20 days within an atmosphere of 40.degree. to 70.degree. C. The wheat flour is then directly put into use or mixed with unmatured wheat flour.
(ii) Heat-treating method as disclosed in U.S. Pat. No. 3,428,461
In this method, the wheat flour is heat-treated for a period of between 1 minute and 17 hours at a temperature of 150.degree. to 360.degree. F.
(iii) Quality improvement by addition of agent or contact with gas.
Methods have been proposed and partly put into practical use in which the wheat flour is improved by addition of agents such as potassium bromate (KBrO.sub.3), ammonium persulfate ((NH.sub.4).sub.2 SO.sub.5), benzoyl peroxide or the like, as well as methods in which a gas such as chlorine dioxide (ClO.sub.2) or nitrogen dioxide (NO.sub.2) is brought into contact with the wheat flour.
The early maturing process mentioned in item (i) above can make the maturing period considerably shorter than that of the natural maturing method which requires preservation of the wheat flour for 2 to 3 months. This method, however, suffers from various drawbacks inherent in the maturing process: namely, necessity for troublesome wrapping of the wheat flour, necessity for a storage space for preservation and so forth, resulting in an impractically low efficiency of the work. Thus, this method is uneconomical as regards both time and space.
The heat-treating method mentioned in the item (ii) above is still unsatisfactory in that it cannot provide remarkable improvement in the water holding capacity and viscoelasticity of the wheat flour, although it can reform strong flour into a powder equivalent of wheat flour for making cakes.
The third method mentioned in the item (iii) above also involves problems as follows. Namely, potassium bromate is highly toxic. In fact, the minimum lethal dose of potassium bromate for oral administration on rabbits is 250 to 580 mg/kg (rabbit dies in 12 hours). Consumption of potassium bromate in excess of a predetermined limit causes lesions in the central nervous system of human. Therefore, it is necessary to pay specific attention to strictly observing use standards. Ammonium persulfate is not so toxic as potassium bromate but adversely affects the human body to cause, for example, allergic disease and dermatopathy when taken in a large amount. Ammonium persulfate, therefore, has to be handled with greatest care. The use of oxidizing agents such as benzoyl peroxide, chlorine dioxide and so forth leads to various problems. For instance, an excessive application of these oxidizing agent causes exccssive oxidation and, hence, an excessive maturing of the wheat flour. In consequence, the extensibility of gluten is decreased and the appearance of the secondary product is deteriorated. The excessive use of oxidizing agent is also undesirable from the viewpoint of nutrition because it may cause decomposition of useful vitamines. In addition, these dioxidizing agents are rather difficult to handle and have unfavourable effects on the human body which cannot be ignored.
Nitrogen dioxide gas can provide only a small maturing or bleaching effect. For attaining a sufficient maturing or bleaching effect, it is necessary to use a large amount of nitrogen dioxide gas. This, however, is inevitably accompanied by a degradation in the hue of the secondary products.
It is true that the use of the quality improvement agents and the use of treating gases such as nitrogen dioxide gas advantageously shortens the processing time to less than that in the natural maturing method mentioned before. Such methods, however, involve a risk that the agent or gas which inevitably remains in the products will have an unexpected unfavourable effect on the human body as explained above.
Under these circumstances, there is an increasing demand for development of a method which can improve the quality of wheat flour in a short period of time without using any agent noxious from the viewpoint of food sanitation and safety.
In response to this demand, the present inventors have accomplished the present invention through an intense study in search of a method permitting an improvement of the quality of wheat flour without requiring the use of quality improving agents or treating gases harmful from the viewpoint of food sanitation and safety.
At the same time, the present inventors have made an investigation to search out prior techniques relating to the use of non-equilibrium plasma. As a result, it was confirmed that no approach has been made up to now to the application of non-equilibrium plasma to the processing of foodstuffs, particularly wheat flour, for the increase of the value added to the flour, although such application nowadays is found increasingly wide use for enhancing the value added to various products, e.g., for improvement of the hydrophilic and adhesive characteristics of high polymers, surface hardening treatment for metallic materials, application to processes for manufacturing integrated circuits, and so forth.